Tehran was surely hoping that by accepting the deal, it would head off a new sanctions resolution being drafted by the U.N. Security Council. The would-be mediators, Turkey and Brazil, were hoping to buff their credentials as leaders of a new "nonaligned movement."

The new U.N. resolution won't stop Iran's nuclear program any more than the previous three did. The draft discusses energy sanctions and an arms embargo, but it doesn't specify enforcement mechanisms. The United States and its allies will top up the U.N. sanctions with some tougher measures of their own, but those won't be enough to halt Tehran either.

What's important about the unified U.N. stand is that it will force Iran back to the bargaining table if it wants to avoid growing diplomatic isolation from the world's superpowers. Yes, Tehran can claim that it has support from two of the world's rising nations, Turkey and Brazil, which it will tout as allies against the great satans of the Security Council. But realistically, the Iranians know that having lost Russia and China on sanctions, they are on shaky ground.

The Obama administration has been calculating that unity among the "P-5" (diplo-speak for the five permanent Security Council members) is more important than the details of the sanctions resolution, and this week's events showed that this strategy was right. The draft resolution was the payoff for President Obama's eight discussions about Iran with Russian President Dmitry Medvedev over the past year, and for the administration's nascent partnership with the world's true rising power, China.

What's next in this diplomatic game of chicken? The answer, says a senior administration official, is that Iran must address two key issues that were part of the enrichment deal floated in October in Geneva. It called for Iran to turn over 2,640 pounds of low-enriched uranium and receive from abroad, in exchange, 260 pounds of uranium that has been enriched to 20 percent, for use in the Tehran Research Reactor for medical isotopes. The new wrinkle in the Turkish-Brazilian version announced Monday was that the Iranian fuel would be shipped to Turkey rather than Russia.

To make the deal fly, said the senior U.S. official, Iran must first meet with the P-5 and Germany for detailed discussions, as specified in the original Geneva proposal. And second, Tehran must agree to forgo its own enrichment to 20 percent. Iran's assertion that it had a unilateral right to continue enrichment to the 20 percent level, regardless of the exchange of fuel, cemented Russian and Chinese support for sanctions, said the senior official.

The problem with this protracted process of bargaining is that the clock is ticking, with Iran moving toward nuclear-weapons capability even as it haggles on the diplomatic front. As Iran plays the game, "yes" and "no" are never final; negotiators walk away from the table only to return; face-saving compromises are floated, rejected and then re-floated. It's likely that this enervating bargaining will end when Iran announces -- surprise! -- that it has all the elements for a nuclear weapon and is now a de facto nuclear state.

The chances of avoiding this bad outcome are fractionally better today than they were a week ago, for one reason: When it came to the crunch this time, Russia and China refused to be enablers for Tehran. By endorsing U.N. sanctions, they stood with the nations that want to prevent Iran from having nuclear weapons.